Straight-cut motor shaft with pinned eccentric

ABSTRACT

An electro-hydraulic pump assembly for a controlled braking system utilizes an eccentric pump drive apparatus including a pump drive shaft having a first end thereof adapted for attachment of an eccentric, and an eccentric attached to the first end of the pump drive shaft. The pump drive shaft defines a centerline thereof, and a bore extending from a first end of the shaft parallel to and displaced an offset distance from the centerline. The eccentric includes a drive element and a stem extending from the drive element for a press fit into the bore of the shaft. The bore extends into the shaft beyond the end of the stem of the eccentric, forming a void inside the shaft for balancing the shaft so that no counterweights need to be added to the eccentric drive apparatus. The pump drive shaft and eccentric are fabricated from straight-cut cylindrical stock by simple turning, drilling, and cylindrical grinding operations.

TECHNICAL FIELD OF THE INVENTION

[0001] This invention relates to eccentric driven pumps, and more particularly to electric motor driven eccentric pumps for controlled brake systems in vehicles.

BACKGROUND OF THE INVENTION

[0002] Modem vehicle brake systems having controlled braking functions, such as anti-lock, traction control, or dynamic stability control, typically include a controlled braking pump that supplies pressurized hydraulic fluid to the brake system during operation in one or more of the controlled braking functions. Such controlled braking pumps typically include one or more positive displacement, reciprocating piston assemblies, driven by an eccentric on a pump drive shaft that is in turn driven by an electric motor.

[0003] In a typical prior controlled braking electro-hydraulic pump assembly 10, as shown in FIG. 1, the pump drive shaft 12 extends from the rotor 14 of an electric motor 16. The electric motor 16 is adapted for attachment to a pump housing 18. The pump drive shaft 12 is a single piece, machined and ground in multiple operations to define a stepped distal end thereof, including an eccentric 20 for receipt of a needle bearing 22 adapted to bear against and drive one or more piston assemblies 24. Two thrust washers 26 are pressed onto the eccentric 20 on either side of the needle bearing 22, for retaining the needle bearing on the eccentric 20. In order to compensate for the material removed from the drive shaft 12 in forming the eccentric, and balance the rotating assembly formed by the drive shaft 12 and the motor rotor 14, extra partial laminations or a brass counterweight 28 is attached to one end the rotor 14 at a position diametrically opposite from the direction that the eccentric 20 is offset from the centerline 30 of the pump drive shaft 12.

[0004] While a controlled braking pump assembly 10 constructed as described above functions well, there are several areas in which it would be desirable to make improvements for facilitating manufacturing, reducing cost, and allowing a single same motor and drive shaft assembly to be used for a family of pumps having different displacement requirements. The multiple machining and grinding operations necessary for forming the eccentric 20 are costly. Changing the distance ‘d’ that the eccentric 20 is offset from the centerline 30 of the drive shaft 12, to generate a shorter or longer stroke of the piston assemblies 24 in controlled braking pump assemblies 10 of different displacements, requires significant changes in machining set-ups and tooling. Changing the offset distance ‘d’ also changes the size of the counterweight 28 required for balancing the rotating assembly, thereby necessitating the fabrication and stocking of motors 16 having a different shaft 12, rotor 14 and counterweight 28 for each desired displacement necessary for supporting alternate vehicle applications.

[0005] What is needed, therefore, is an improved apparatus and method for providing an eccentric pump drive shaft and controlled braking pump addressing one or more of the problems described above.

SUMMARY OF THE INVENTION

[0006] Our invention provides an improved eccentric pump drive apparatus and controlled braking pump assembly, through the use of an eccentric pump drive apparatus having a pump drive shaft with a first end thereof adapted for attachment of an eccentric and an eccentric attached to the first end of the pump drive shaft. The eccentric pump drive apparatus may include an easily fabricated straight-cut pump drive shaft and a stepped eccentric element pinned to one end of the shaft.

[0007] In one form of our invention the pump drive shaft defines a centerline thereof and a bore extending from the first end of the shaft parallel to and displaced an offset distance from the centerline. The eccentric includes a drive element thereof and a stem extending from the drive element for a press fit into the bore of the shaft.

[0008] The eccentric defines a mass offset from the centerline of the shaft, and the bore may include a portion of the bore extending into the shaft a distance beyond the stem to such a length from the first end of the shaft that a void is formed inside of the shaft for rotationally balancing the eccentric drive apparatus about the centerline of the shaft. The eccentric drive apparatus may include a bearing on the drive element of the eccentric. Where there is a bearing on the drive element, the eccentric and bearing define a mass offset from the centerline of the shaft, and the portion of the bore extending into the shaft may extend beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft, to thereby compensate for the offset mass of the eccentric and bearing. The eccentric pump drive apparatus may include a motor rotor attached to the shaft.

[0009] Our invention may also take the form of a pump including an eccentric drive apparatus according to our invention, or a method for fabricating an eccentric pump drive apparatus.

[0010] The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is cross-section of a prior controlled braking pump assembly having an eccentric drive apparatus;

[0012]FIG. 2 is a cross-section of a controlled braking pump assembly and eccentric pump drive apparatus, according to our invention; and

[0013]FIG. 3 is a perspective view of an eccentric for the eccentric pump drive apparatus in the pump of FIG. 2.

DETAILED DESCRIPTION

[0014]FIG. 2 shows an exemplary embodiment of our invention in the form of a pump 40 for a controlled braking system. The pump assembly 40 includes an electric motor 42 having a rotor 44 defining an axis of rotation 46, and an eccentric pump drive apparatus 48. The eccentric pump drive apparatus 48 includes a pump drive shaft 50 attached to the rotor 44 for rotation about the axis of rotation 46, and having a first end 52 thereof adapted for attachment of an eccentric 54, and an eccentric 54 attached to the first end 52 of the pump drive shaft 50 by a press fit.

[0015] The pump drive shaft 50 defines a centerline 56 thereof, extending along the axis of rotation 46 and a bore 58 extending from the first end 52 of the shaft 50 parallel to and displaced an offset distance ‘d’ from the centerline 56. The eccentric 48 includes a drive element 60, and a stem 62 extending from the drive element 60. A needle bearing 64 is slip fitted onto the drive element 60. The stem 62 is then press fitted into the bore 58 of the shaft 50. The distal end 52 of the eccentric 54 includes a flange 66 for retaining the bearing 64 on the drive element 60 of the eccentric 54. As shown schematically in FIG. 2, the motor 42 is attached to a pump housing 68, including a pair of reciprocating piston assemblies 70 that are operatively connected to bear against and be driven by the needle bearing 64.

[0016] The eccentric 54 and bearing 64 define a mass that is offset from the centerline 56 of the shaft 50. A portion 72 of the bore 58 extends into the shaft 50 beyond the stem 62 a distance ‘I’ to create a void inside the shaft 50 of sufficient volume that the eccentric pump drive apparatus 48 is rotationally balanced about the centerline 56 of the shaft 50, to thereby compensate for the offset mass of the eccentric 54 and bearing 64.

[0017] By balancing the drive apparatus 48 using the void inside of the shaft 50, according to the invention, the counterweights that had to be attached to the rotor for balancing prior eccentric drive mechanisms and pumps can be eliminated, thereby reducing the complexity and weight and facilitating fabrication of the electro-hydraulic pump assembly 40.

[0018] The shaft 50 can be fabricated from a straight-cut length of cylindrical material, with the bore 58 drilled into one end 52 at a desired offset distance ‘d’ from the centerline 56 of the shaft. The offset distance ‘d’ can be readily changed, without the major changes in tooling required in prior eccentric drive mechanisms, to move the drive element 60 farther in or out from the centerline 56 of the shaft 50 to respectively reduce or increase the effective displacement of the pump assembly 40. As shown in FIG. 3, the stern 62, drive element 60, and flange 66 of the eccentric 20 can be fabricated as a stepped pin, using simple turning operations on an automated lathe or a screw machine.

[0019] While the embodiments of the present invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention.

[0020] The scope of the invention is indicated in the appended claims. We intend that all changes or modifications within the meaning and range of equivalents are embraced by the claims. 

We claim:
 1. An eccentric pump drive apparatus comprising: a pump drive shaft having a first end thereof adapted for attachment of an eccentric; and an eccentric attached to the first end of the pump drive shaft.
 2. The eccentric pump drive apparatus of claim 1 wherein the eccentric is attached to the first end of the shaft with a press fit.
 3. The eccentric pump drive apparatus of claim 1 wherein: the shaft defines a centerline thereof and a bore extending from the first end of the shaft parallel to and displaced an offset distance from the centerline; and the eccentric includes drive element thereof and a stem extending from the drive element for a press fit into the bore of the shaft.
 4. The eccentric pump drive apparatus of claim 3 including a motor rotor attached to the shaft.
 5. The eccentric pump drive apparatus of claim 3 further including a bearing on the drive element of the eccentric.
 6. The eccentric pump drive apparatus of claim 5 including a motor rotor attached to the shaft.
 7. The eccentric pump drive apparatus of claim 5 wherein the bearing is a needle bearing press fitted onto the drive element.
 8. The eccentric pump drive apparatus of claim 7 wherein the eccentric includes a flange at the distal end thereof for retaining the bearing on the drive element of the eccentric.
 9. The eccentric pump drive apparatus of claim 3 wherein the eccentric defines a mass offset from the centerline of the shaft, and the bore includes a portion thereof extending into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.
 10. The eccentric pump drive apparatus of claim 9 including a motor rotor attached to the shaft.
 11. The eccentric pump drive apparatus of claim 9 wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the portion of the bore extending into the shaft extends a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft, to thereby compensate for the offset mass of the eccentric and bearing.
 12. The eccentric pump drive apparatus of claim 11 including a motor rotor attached to the shaft.
 13. A pump assembly comprising: an electric motor having a rotor defining an axis of rotation; and an eccentric pump drive apparatus including a pump drive shaft attached to the rotor for rotation about the axis of rotation and having a first end thereof adapted for attachment of an eccentric, and an eccentric attached to the first end of the pump drive shaft.
 14. The pump assembly of claim 13 wherein the eccentric is attached to the first end of the shaft with a press fit.
 15. The pump assembly of claim 13 wherein: the shaft defines a centerline thereof extending along the axis of rotation and a bore extending from the first end of the shaft parallel to and displaced an offset distance from the centerline; and the eccentric includes a drive element thereof and a stem extending from the drive element for a press fit into the bore of the shaft.
 16. The pump assembly of claim 15 wherein the eccentric defines a mass offset from the centerline of the shaft, and the bore includes a portion thereof extending into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.
 17. The pump assembly of claim 15 wherein the eccentric drive element includes a bearing on the drive element of the eccentric.
 18. The pump assembly of claim 17 wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the portion of the bore extends into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft, to thereby compensate for the offset mass of the eccentric and bearing.
 19. A method for fabricating an eccentric pump drive apparatus, the method comprising: fabricating a pump drive shaft having a first end thereof adapted for attachment of an eccentric, and attaching an eccentric to the first end of the pump drive shaft.
 20. The method of claim 19 wherein the shaft defines a centerline thereof, and the method further comprises: forming a bore in the shaft extending from the first end of the shaft parallel to and displaced an offset distance from the centerline; forming the eccentric to include a drive element thereof and a stem extending from the drive element; and inserting the stem of the eccentric into the bore.
 21. The method of claim 20 wherein the drive element defines a mass, and the method comprises: extending the bore into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.
 22. The method of claim 21 further comprising attaching a motor rotor to the shaft.
 23. The method of claim 21 further comprising installing a bearing on the drive element of the eccentric.
 24. The method of claim 23 wherein the eccentric and bearing define a mass offset from the centerline of the shaft, and the method comprises: extending the bore into the shaft a distance beyond the stem to such a length from the first end of the shaft that the eccentric pump drive apparatus is rotationally balanced about the centerline of the shaft.
 25. The method of claim 24 further comprising attaching a motor rotor to the shaft. 